PURPOSE: To efficiently operate a refrigeration cycle even if power recovery is small by making compact an auxiliary compressor for power recovery.

CONSTITUTION: A refrigeration cycle comprises a main compressor 91, condenser 92, expansion machine 93, evaporator 94, and auxiliary compressor 1. The compressor 1 is installed in a by-pass line 32 provided in parallel with the compressor 91. The compressor 1 is driven by the power taken out in a pressure reducing process of the machine 93. Part of refrigerant evaporated by the evaporator 94 is supplied to the compressor 1. In this manner, only refrigerant in quantity corresponding to the recovered power is compressed by the compressor 1, so that its size can be reduced. As a result, even if power recovery is small, the refrigeration cycle can accomplish sufficient performance.